Case IH 517678-06 - BCM – BCM: Trailer brake lamps - short circuit to ground

The control module has detected that the voltage intended for the trailer's brake lights is finding a direct path to ground (0 ohms or very low resistance) before reaching the load (the bulbs). This is typically caused by chafed wire insulation touching the chassis, a melted connector, or an internally shorted bulb socket.

• MAGNUM AFS Connect
• Magnum AFS Connect 180
• Magnum AFS Connect 200
• Magnum AFS Connect 220
• Magnum AFS Connect 240
• Magnum AFS Connect 250
• Magnum AFS Connect 280
• Magnum AFS Connect 310
• Magnum AFS Connect 340
• Magnum AFS Connect 380
• Steiger AFS Connect

1. 1

   Isolate the tractor by disconnecting the trailer plug from the rear 7-pin receptacle, clearing the code, and applying the brakes. If the code returns, the short is on the tractor; if not, it is on the trailer.

2. 2

   Inspect the tractor's rear trailer plug receptacle for heavy corrosion, water intrusion, or bent pins bridging the brake lamp pin to the ground pin.

3. 3

   If the fault is on the trailer, inspect the wiring harness where it routes along the trailer frame for pinched wires, rubbed insulation, or chafing near metal gussets.

4. 4

   Remove the lenses on the trailer brake lights and check for internally shorted bulbs, melted sockets, or a ground wire touching the positive terminal inside the housing.

5. 5

   If the fault is on the tractor, use a multimeter to check for continuity to ground on the brake lamp circuit pin at the BCM connector, and trace the harness to the rear receptacle looking for chafed spots.

1. 1

   Disconnect Power

   Turn off the battery disconnect switch to prevent further electrical damage while repairing the circuit.

2. 2

   Repair Damaged Wiring

   If a chafed wire is found (either on the tractor harness or trailer frame), cut out the damaged section.

3. 3

   Splice and Seal

   Strip the wire ends and use a marine-grade crimp connector. Solder the connection and seal it with waterproof heat-shrink tubing to prevent moisture from causing future shorts.

4. 4

   Replace Receptacle/Plug (If Applicable)

   If the short is caused by a melted or heavily corroded 7-pin connector, cut the wires back to clean copper and wire in a new SAE J560a receptacle or plug.

5. 5

   Re-route Harness

   Secure the repaired wiring harness with zip ties or loom clamps, ensuring it is routed away from sharp metal edges, pinch points, and moving suspension/hitch components.

6. 6

   Clear Codes

   Reconnect the battery, plug the trailer back in, and use the CNH EST (Electronic Service Tool) to clear the inactive 517678-06 fault code from the BCM. Test the brake pedals to confirm the lights illuminate without triggering the code.